GDB is running a deleted executable file - compilation

Question

I was debugging an executable_file which is generated from C++ codes. When I was in the middle of a GDB session, I changed the source.cpp files and recompiled them to regenerate a new executable_file. Now, GDB is running the old deleted executable_file, even though I have deleted that old file from my system. How this is possible? How can I force GDB to run the new executable_file?
UPDATE:
After restarting the system, everything worked fine for the first compilation, and I could run the new executable_file. But I am observing the same issue for the next compilations. Nevertheless, when I remove executable.o and recompile everything look fine.
Is this because of an issue in my makefile? Or I have broken something in my Unix system?

Answer 1

When you delete a file that's being used, Unix will remove the file from the directory, but the file will still exist until the last user is done with it.
To force gdb (or any application in this situation) to use the newest version, restart the application (or reload the file into the application if that's an option).
As a point of comparison, if you were running on Windows, you'd get an error regenerating an executable while the file is already in use.
Update: If you're doing this frequently, consider modifying your makefile to append a revision number to the generated executable. Each executable would have a unique name, and this would help avoid confusion about which file you're using.

Answer 2

Once a program, library, etc. is loaded into memory, it can be deleted but still be able to run. Once the program is closed and restarted, you will be running the new program.
An instance of where this is problematic is the many times I've deleted a library or executable that my Linux box needed to run. Once I restart my computer, I soon realize that I messed it up ...
Fun times.
By way of example,
/*
Compile me.
Run the executable.
While the program is running, delete the executable/binary.
The program will continue printing the message.
*/
#include <stdio.h>
#include <unistd.h>
int main () {
while (1) {
printf("I'm still running.\n");
sleep(2);
}
return 0;
}
To answer your question, close the currently running gdb session. Then start a new one, using your new executable.
PS: If you started it before you deleted it, you're still running it. (Where it is the old program.)